Slo-Mo Video Shows Frog's Sticky Saliva Snaring Prey

A super-soft tongue and spit that changes properties combine to help amphibians hang onto food and may even help people create new adhesives.

Reversible saliva and a super-soft tongue work together to help frogs snare their prey at lightning speed and then hold onto their meals.

So say researchers from Georgia Institute of Technology, who used slow-motion video to get a better understanding of the physics of a frog's tongue as the amphibian strikes a luckless cricket, into the bargain studying saliva from the animal and also gauging the softness of its tongue.

In doing so, the scientists uncovered a complex process in which the frog's spit changes its texture by turns during prey capture. Their findings have been published in a study in the Journal of the Royal Society Interface.

First, the frog's tongue zooms outward toward its target cricket, uncoiling like a tight spring, faster than the blink of a human eye. When the tongue strikes the cricket, the team found, a layer of saliva flows into the insect's crevices, while maintaining high adhesion. As the tongue retracts back to the frog's mouth, that saliva layer holds fast and the cricket has no way out of its dilemma.

The spit's "reversibility" occurs at the end. The researchers learned that the frog's saliva is sticky and viscous while the tongue is snapping out and reeling in the bug but then becomes thin and watery once the cricket is safely in the amphibian's mouth.

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The scientists liken the process to paint being applied to a wall – spreading with ease during brush strokes but sticking once the brush is pulled away.

"For frogs, saliva seeps easily when it hits the insect, then thickens up during retraction," said study lead Alexis Noel in a statement.

For its part, the tongue of a frog turned out to be exceedingly soft – 10 times softer than the human tongue, as soft as brain tissue, according to the scientists. That softness, combined with the spit, creates powerful adhesion between tongue and prey, they found. The extreme softness also helps the tongue coil and change shape when it strikes prey and then retracts toward the mouth.

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Frogs might not be the only ones to gain from all of this stickiness. (Only the cricket gets nothing out of this research.) The study could lead to new adhesives that can quickly reverse their viscosity.

"Most adhesives that have been created are stiff, especially tape," explained Noel's adviser, Georgia Tech engineering professor David Hu. "Frog tongues can attach and reattach with soft, special properties that are extremely stickier than typical materials. Perhaps this technology could be used for new Band-Aids. Or it could be used to create new materials in soft manufacturing."

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